1. Field of the Invention
The invention relates to a rotor for an electric motor.
2. Description of Prior Art
Electric motors generally have a rotor and a stator. So-called brushless DC motors, which are also referred to as BLDC motors, are becoming increasingly prevalent in the automotive engineering sector. Such BLDC motors are synchronous motors driven by a direct current and have an electronic commutation device, instead of mechanical commutators and brushes.
In this way, relatively low levels of friction in comparison with motors with commutators and brushes are ensured, which therefore has a positive effect on efficiency. Furthermore, so-called brush sparking can be avoided, which firstly results in electrical losses and secondly also contributes to increased mechanical wear.
The rotor, for example of BLDC motors, has a rotor basic body, on which permanent magnets are arranged. Owing to the fact that no coil windings are located on the rotor, the windings are not subject to centrifugal forces. In addition, windings are arranged only on the stator, with the result that no air cooling is required in the region of the rotor for cooling purposes and therefore the inner region, in particular the region of the rotor in which the permanent magnets are arranged, can be encapsulated from the outside and can thus also be protected from dirt particles and other external particles.
DE 10 2008 043 144 A1 discloses an electric machine in the form of a claw-pole generator. A rotor has claw-pole fingers. Interspaces in which permanent magnets are arranged are located between the individual axially conical claw-pole fingers of the claw poles. The permanent magnets reduce leakage flux. The permanent magnets are fastened in the interspaces between the individual claw-pole fingers by holding elements. For this purpose, the holding elements are inserted into pole slots in the claw-pole fingers.
DE 198 32 253 A1 discloses an electric motor with a rotor and a stator. The rotor has at least two permanently magnetic magnet shells that are separate from one another. The stator is arranged concentrically around the rotor and has electrical coils. A holding element consisting of magnetically nonconductive material for holding the magnet shells is provided. The magnet shells bear on their radially outer side against in each case at least one holding shell. The holding shell is preferably a material with a high magnetic conductivity. The holding shells of two magnet shells are spaced apart from one another and are pretensioned in the direction of the rotor axis by the holding element arranged in a lateral region of the magnet shells.
DE 10 2008 048 944 A1 discloses an AC generator with a rotor and a stator. The stator is arranged radially outside the rotor and extends axially along the length of the rotor and extends around the circumference of the rotor. The stator and the rotor are arranged in a housing. The rotor comprises one or more permanent magnets, which are arranged in magnet slots between rotor poles. The rotor comprises a rotor core and one or more magnet slots between rotor poles. The respective magnet slot has a tapering cross section such that the slot width increases as the radial extent of the slot increases from the shaft. A slot lip extends on the circumference of at least one of the rotor poles in the direction of an opposite rotor pole at a radially outer end of the rotor poles. A holding element is provided for locking the magnet in the magnet slot in a radial direction. The holding element is arranged in the magnet slot radially between the magnet and the slot lip.
DE 298 01 184 U1 discloses a generator for a motor vehicle with an excitation system comprising a multiplicity of electrically excited individual poles in a rotor, in the form of claw poles excited by at least one common field coil. Permanent magnets are introduced into the free spaces between the claw poles pointing axially towards one another of the pole plates fitted on the axial ends of the rotor, for compensation of the magnetic leakage flux. The permanent magnets are supported by a holder with respect to centrifugal forces and are held thereby. The holder is formed from two nonmagnetic accommodating cages each having a ring-shaped disk. Multiple chamfered strip sections are formed integrally on the ring-shaped disk and form in each case one accommodating chamber for at least one permanent magnet per free space. Each accommodating chamber is closed at least towards the axial center of the rotor and towards the centrifugally loaded side of the free spaces. The accommodating chamber is fixed on the claw poles and/or the pole plates.